Matt Ridley

likelihood of a heart attack than obesity, smoking or high blood pressure. Somebody in a low-grade job, such as a janitor, was nearly four times as likely to have a heart attack as a permanent secretary at the top of the heap.

Indeed, even if the permanent secretary was fat, hypertensive or a smoker, he was still less likely to suffer a heart attack at a given age than a thin, non-smoking, low-blood-pressure janitor. Exactly the same result emerged from a similar study of a million employees of the Bell Telephone Company in the 1960s.3

Think about this conclusion for a moment. It undermines almost everything you have ever been told about heart disease. It relegates cholesterol to the margins of the story (high cholesterol is a risk factor, but only in those with genetic predispositions to high cholesterol, and even in these people the beneficial effects of eating less fat are small). It relegates diet, smoking and blood pressure - all the physiological causes so preferred by the medical profession — to secondary causes. It relegates to a footnote the old and largely discredited notion that stress and heart failure come with busy, senior jobs or fast-living personalities: again there is a grain of truth in this fact, but not much. Instead, dwarfing these effects, science now elevates something non-physiological, something strictly related to the outside world: the status of your job. Your heart is at the mercy of your pay grade. What on earth is going on?

The monkeys hold the clue. The lower they are in the pecking 156 G E N O M E

order, the less control they have over their lives. Likewise in the civil service, Cortisol levels rise in response not to the amount of work you do, but to the degree to which you are ordered about by other people. Indeed, you can demonstrate this effect experimentally, just by giving two groups of people the same task to do, but ordering one group to do the task in a set manner and to an imposed schedule.

This externally controlled group of people suffers a greater increase in stress hormones and rise in blood pressure and heart rate than the other group.

Twenty years after the Whitehall study began, it was repeated in a department of the civil service that then began to experience privatisation. At the beginning of the study, the civil servants had no notion of what it meant to lose their jobs. Indeed, when a questionnaire was being piloted for the study, the subjects objected to a question that asked if they feared losing their jobs. It was a meaningless question in the civil service, they explained: at worst they might be transferred to a different department. By 1995 they knew exactly what losing their jobs meant; more than one in three had already experienced it. The effect of privatisation was to give everybody a feeling that their lives were at the mercy of external factors. Not surprisingly, stress followed and with stress came ill health - far more ill health than could be explained by any changes in diet, smoking or drinking.

The fact that heart disease is a symptom of lack of control explains a good deal about its sporadic appearance. It explains why so many people in senior jobs have heart attacks soon after they retire and

'take it easy'. From running offices they often move to lowly and menial jobs (washing dishes, walking the dog) in domestic environments run by their spouses. It explains why people are capable of postponing an illness, even a heart attack, until after a family wedding or a major celebration — until the end of a period of busy work when they are in control of events. (Students also tend to go down with illnesses after periods of acute exam pressure, not during them.) It explains why unemployment and welfare dependency are so good at making people ill. No alpha-male monkey was ever such an S T R E S S 157

intransigent and implacable controller of subordinates' lives as the social services of the state are of people dependent on welfare. It may even explain why modern buildings in which the windows cannot be opened make people sicker than older buildings in which people have more control over their environment.

I am going to repeat myself for emphasis. Far from behaviour being at the mercy of our biology, our biology is often at the mercy of our behaviour.

What is true of Cortisol is also true of other steroid hormones.

Testosterone levels correlate with aggression, but is that because the hormone causes aggression, or because release of the hormone is caused by aggression? In our materialism, we find the first alternative far easier to believe. But in fact, as studies of baboons demonstrate, the second is closer to the truth. The psychological precedes the physical. The mind drives the body, which drives the genome.4

Testosterone is just as good at suppressing the immune system as Cortisol. This explains why, in many species, males catch more diseases and have higher mortality than females. This immune suppression applies not just to the body's resistance to micro-organisms, but to large parasites, too. The warble fly lays its eggs on the skin of deer and cattle; the maggot then burrows into the flesh of the animal before returning to the skin to form a nodule in which to metamorphose into a fly. Reindeer in northern Norway are especially troubled by these parasites, but males noticeably more than females.

On average, by the age of two, a male reindeer has three times as many warble-fly nodules in its skin as a female reindeer, yet castrated males have the same number as females. A similar pattern can be found for many infectious parasites, including, for instance, the protozoan that causes Chagas' disease, the affliction widely believed to explain Charles Darwin's chronic illnesses. Darwin was bitten by the bug that carries Chagas' disease while travelling in Chile and some of his later symptoms fit the disease. If Darwin had been a woman, he might have spent less time feeling sorry for himself.

Yet it is to Darwin that we must turn for enlightenment here.

The fact that testosterone suppresses immune function has been 1 5 8 G E N O M E

seized upon by a cousin of natural selection known as sexual selection and ingeniously exploited. In Darwin's second book on evolution, The descent of man, he put forward the notion that, just as a pigeon breeder can breed pigeons, so a female can breed males. By consistently choosing which males to mate with over many generations, female animals can alter the shape, colour, size or song of males of their species. Indeed, as I described in the chapter on chromosomes X and Y, Darwin suggested that this is exactly what has happened in the case of peacocks. It was not until a century later, in the 1970s and 1980s, that a series of theoretical and experimental studies demonstrated that Darwin was right, and that the tails, plumes, antlers, songs and size of male animals are bred into them by consistent trends of passive or active female choice, generation after generation.

But why? What conceivable benefit can a female derive from picking a male with a long tail or a loud song? Two favourite ideas have dominated the debate, the first being that the female must follow the prevailing fashion lest she have sons that are not themselves attractive to females who follow the prevailing fashion. The second idea, and the one that I propose to consider here, is that the quality of the male's ornament reflects the quality of his genes in some way. In particular, it reflects the quality of his resistance to prevailing infections. He is saying to all who would listen: see how strong I am; I can grow a great tail or sing a great song, because I am not debilitated by malaria, nor infected with worms. And the fact that testosterone suppresses the immune system is actually the greatest possible help in making this an honest message. For the quality of his ornaments depends on the level of testosterone in his blood: the more testosterone he has, the more colourful, large, songful or aggressive he will be. If he can grow a great tail despite lowering his immune defences, yet not catch disease, he must be impressive genetically. It is almost as if the immune system